Orthodontics involves purposefully moving teeth towards a certain predefined pattern so that the tooth row has an esthetically pleasing look. The condition of crowded or crooked teeth is called malocclusion. Although ancient attempts to correct malocclusion date back to 1000 BC, modern orthodontics began slightly more than a century ago [Proffit et al., (1993) Mosby Year Book: St. Louis. pp. 266–288].
In late 1800s, Edward Angle placed metal bands on the teeth and used continuous wires that fit into the slots of the bands. Elastics were used to apply forces with a result of aligning the teeth along the “track” of the wire. The forces applied by Angle were static and continuous, meaning that once the forces have been generated by elastics, the forces are continuously present unless and until they decayed to nil.
Since Angle's practice, orthodontists have used static forces to induce orthodontic tooth movement. Contemporary orthodontic treatment takes an average of two years to complete in one patient, involving multiple visits and repeated activations; i.e., reasserting the force on the teeth. No one has attempted to determine whether cyclic forces; i.e., forces with rapidly varying magnitude over time, induce more rapid tooth movement than the presently used continuous forces.
Orthodontics involves the use of mechanical forces to move teeth within the jaw bone and therefore, relies on force-induced bone remodeling. A force is a physical quantity and has several essential properties such as the magnitude, direction, point of application and frequency. All these properties of orthodontic forces have been subjects of scientific research and considered in clinical practice of orthodontics with the exception of force frequency. Exclusive use of continuously applied static forces in orthodontics and the resulting lack of consideration of force frequency contradict the overall scientific consensus-based evidence obtained from orthopedic studies of long bones that cyclic forces induce more effective bone remodeling than static forces of matching magnitude.
The main advantage of the current orthodontic technology of using continuously applied static forces to move the teeth towards predetermined positions to achieve esthetically pleasing look is its predictable, albeit slow, outcome, inducing controlled tooth movement towards predetermined position when treatment is carried out by a competent orthodontist. The principal shortcoming of the current technology is its requirement of excessively long treatment duration: approximately two years on average. The essential reason for this excessively long treatment duration is due to a lack of efficiency resulting from the present use of continuously applied static forces.
More specifically, except as described hereinafter, only continuously applied static forces have been studied and/or used in previous studies and clinical practice in orthodontics. First, about 36 percent of the US population receive orthodontic treatments [Brunelle et al., (1996) J. Dent. Res., 75(Spec Iss):706–713]. Continuously applied static forces are used on a daily basis for orthodontic tooth movement in these patients. Second, in addition to day-to-day practice of application of continuously applied static forces in clinical orthodontics, orthodontic tooth movement has been simulated in animal models with elastics and coil springs [Reitan (1951) Acta Odont. Scand. Suppl., 6:1–240; Storey et al., (1952) Aust. J. Dent., 56:11–18; Pygh et al., (1982) In Berkivitz et al. (Eds) The Periodontal Ligament in Health and Disease, Pergamon Press, Oxford, England, pp. 269–290; Jager et al., (1993) Histochemistry, 100:161–166; Ashizawa et al., (1998) Arch Oral Biol., 43(6):473–484; Gu et al., (1999 Angle Orthod. 69(6):515–522; Melsen (1999) Angle Orthod., 69(2):151–158; Terai et al.,(1999) J. Bone Miner. Res., 14(6): 839–849; Tsay et al., (1999) Am. J. Orthod. Dentofacial Orthop., 115(3):323–330; and Verna (1999) Bone, 24(4):371–379]. Without exception, continuously applied static forces have been used in all these studies.
Although there have been previous attempts to use “intermittent forces”, the nature of the intermittent forces were static forces applied intermittently over time, for instance, two hours on and two hours off [Reitan (1951) Acta Odont. Scand. Suppl., 6:1–240; van Leeuwen et al., (1999) Eur. J. Oral Sci., 107(6):468–474] instead of the hereinafter described cyclic forces that rapidly change magnitude over short time, e.g. several cycles per second. The current technology of continuous, constant and static forces, such as those used in orthodontics, lacks either frequency modulation or change in force magnitude over time.
In addition to a lack of consideration of force frequency in both research studies and clinical practice of orthodontics as described above, both the threshold force and the duration of force application, which are two additional essential properties of a force, are not clearly understood in the field of orthodontics. First, a minimum of 6 hours has been thought to be the threshold below which orthodontic tooth movement does not occur [Proffit et al., (1993) Mosby Year Book: St. Louis. pp. 266–288]. However, this projected minimum threshold of 6 hours per day by Proffit et al. is largely theoretical, as stated in the caption of FIGS. 9–12 on page 275 of that work.
Although empirical clinical experience appears to support the notion that orthodontic forces must be applied beyond certain daily duration in order to induce tooth movement, the precise minimum daily duration is unclear. What appears of more significance than daily minimum duration is the overall duration of orthodontic treatment in association with current technology. The use of cyclic forces in orthodontic tooth movement described hereinafter can significantly shorten the present average two-year duration of orthodontic tooth movement.
Although there are more data on the threshold force magnitude required for tooth movement, the precise threshold is yet to be determined. In general a few hundred grams of force have been implicated to be the threshold for tooth movement. However, there remain projections as “theoretically, there is no doubt that light continuous forces produce the most efficient tooth movement” [Proffit et al., (1993) Mosby Year Book: St. Louis. pp. 266–288]. Although it has been shown that proliferation of periodontal ligament cells is greater in response to continuous forces than to intermittent forces of the same magnitude [Reitan (1951) Acta Odont. Scand. Suppl., 6:1–240], the previously investigated intermittent forces were static forces applied intermittently over time [Reitan (1951) Acta Odont. Scand. Suppl., 6:1–240; van Leeuwen et al., (1999) Eur. J. Oral Sci., 107(6):468–474] instead of the presently proposed cyclic forces that rapidly change magnitude within time units of seconds.
Contemporary orthodontists not only use braces to align the teeth, they also use orthopedic appliances such as headgear and facemask to change the shape of facial bones so that the overall facial shape is esthetically pleasant. The present technology (described hereinafter), in addition to providing a mechanism for rapidly aligning the teeth, also provides pathways by which the shape of facial bones can be rapidly changed, although the precise characteristics of the forces responsible for the two approaches are different. The present invention that is described hereinafter provides for the remodeling of craniofacial bones and treatment of malocclusion through the use of cyclic force application to the region to be remodeled.